Got $10? Then you too can be a venture capitalist

Politicians do it. Charities too. And now for-profit entrepreneurs are tapping the Internet to get small amounts of money from lots and lots of supporters. One part social networking and one part capital accumulation, crowdfunding websites seek to harness the enthusiasm--and pocket money--of virtual strangers, promising them a cut of the returns.

Like a homespun IPO, CatwalkGenius.com helps hoi polloi bankroll upstart fashion designers. British documentary filmmaker Franny Armstrong raised more than £450,000 ($815,000) to finance--and work full time on--The Age of Stupid, which she hopes will premiere at the Sundance Film Festival in January. People who gave 20...